The present invention is directed to a pressure sensor for converting fluid pressures into electric signals and more particularly to a pressure sensor which detects fluid pressures by means of a diaphragm and converts distortions of the diaphragm into electric signals.
This type of pressure sensor generally detects changes in fluid pressure by means of distortions of a diaphragm and generates output signals by means of a strain gauge attached to the diaphragm. In such a pressure sensor, a metal resistance wire such as a nickel-copper wire, a semi-conductor of the piezo-resistance type, or a semi-conductor of the fusion type has been used as the strain gauge. In a strain gauge of the metal resistance type, where the temperature stability will be high, the output voltage will be very small, for example, under 8 mV, the maximum use temperature will be low, for example, on the order of 80.degree. C., and the metal resistance wire is liable to be destroyed due to excessive distortion since its resistance to tension is low. In a strain gauge of the semi-conductor type where the sensibility or rate of the gauge tends to be high, the temperature stability will be low, for example, above 0.1 percent FS/degrees centigrade where FS represents full scale, the maximum use temperature will be low, for example, 100.degree. C., and, it is necessary to take measures for protecting the semi-conductor since the semi-conductor is weak with respect to impulsive forces. Furthermore, such a strain gauge is insulated from the diaphragm by an insulator and is attached to the diaphragm. The strain gauge is generally adhered to the diaphragm by means of adhesive, but the characteristics of the sensors will be varied due to the varying of the adhesive property between the strain gauge and the diaphragm and the characteristics of the sensors will deteriorate as the adhesive ages. Accordingly, the application scope of such a gauge will be rather limited due to the above-mentioned characteristics of the strain gauge.